<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>demo 2-18</title>
	</head>
	<body>
	</body>
	<script>
		var a = 10;
		var b = 20;
		console.log(a,b);
		[a,b] = [b,a];
		console.log(a,b);
	</script>
</html>